Comment 1 for bug 630586

I have these exact symptoms. I'm running Maverick and this started about a week ago after an update. Today I discovered by chance that if I disconnect my USB keyboard before booting, the grub menu appears. I can then connect the keyboard and boot like normal. I've tried it several times with and without the keyboard connected and it's repeatable every time. This has never been a problem before so I don't think it's likely to be a hardware problem.